Mapping the magnetic anisotropy in (Ga,Mn)As nanostructures

Hoffmann, Frank; Woltersdorf, Georg; Wegscheider, Werner; Einwanger, Andreas; Weiss, Dieter; Back, Christian

doi:10.1103/physrevb.80.054417

Cited by 17 publications

(10 citation statements)

References 15 publications

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“…2b ). Whereas, as for small damping and if the magnetization M being parallel to the externally applied magnetic field, a non-zero phase shift would be expected and the line shape of FMR spectrum does not exclusively correspond to imaginary magnetic susceptibility, as follows from LLG equation, but represents a mixture of imaginary and the real part of the susceptibility 41 . Given the asymmetric nature of the real part of the dynamic susceptibility as inferred from LLG, we conclude that the asymmetric profile at moderate electric fields in Fig.…”

Section: Resultsmentioning

confidence: 99%

Electric tuning of magnetization dynamics and electric field-induced negative magnetic permeability in nanoscale composite multiferroics

Jia

Wang

Jiang

et al. 2015

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Steering magnetism by electric fields upon interfacing ferromagnetic (FM) and ferroelectric (FE) materials to achieve an emergent multiferroic response bears a great potential for nano-scale devices with novel functionalities. FM/FE heterostructures allow, for instance, the electrical manipulation of magnetic anisotropy via interfacial magnetoelectric (ME) couplings. A charge-mediated ME effect is believed to be generally weak and active in only a few angstroms. Here we present an experimental evidence uncovering a new magnon-driven, strong ME effect acting on the nanometer range. For Co92Zr8 (20 nm) film deposited on ferroelectric PMN-PT we show via ferromagnetic resonance (FMR) that this type of linear ME allows for electrical control of simultaneously the magnetization precession and its damping, both of which are key elements for magnetic switching and spintronics. The experiments unravel further an electric-field-induced negative magnetic permeability effect.

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Section: Resultsmentioning

confidence: 99%

Electric tuning of magnetization dynamics and electric field-induced negative magnetic permeability in nanoscale composite multiferroics

Jia

Wang

Jiang

et al. 2015

Sci Rep

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“…10 To compute the exchange field, we used literature data for (Ga,Mn)As, in terms of the spin stiffness A = 4 × 10 −8 erg/cm, 29 the uniaxial anisotropy constant K U = −1.1 × 10 3 erg/cm 3 , and the cubic anisotropy constant K C = 2.2 × 10 3 erg/cm 3 . 31 Because of the strong cubic anisotropy we can consider K eff ≈ K C /4. 29 The (Ga,Mn)As saturation magnetization was determined by SQUID to be M = 38 G (at T = 12.5 K) for 12% Mn and 18 G (at T = 10 K) for 6% Mn (both 30 nm thickness).…”

Section: B Magnetometrymentioning

confidence: 99%

Reorientation transition of the magnetic proximity polarization in Fe/(Ga,Mn)As bilayers

et al. 2012

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Recently, it has been observed that thin ferromagnetic Fe films deposited on top of (Ga,Mn)As layers induce a significant proximity polarization in the (Ga,Mn)As film even at room temperature. Furthermore, it was found that a thin interfacial region of the (Ga,Mn)As film is coupled antiferromagnetically to the Fe layer. Here we report a series of combined x-ray magnetic dichroism and superconducting quantum interference device magnetometer measurements for Fe/(Ga,Mn)As bilayers where the (Ga,Mn)As layer thickness is varied between 5 and 50 nm. We find a reorientation transition of the magnetic proximity polarization as a function of the (Ga,Mn)As thickness. The data are compared to results obtained performing ab initio calculations. A varying concentration of Mn interstitials as a function of (Ga,Mn)As layer thickness is responsible for this reorientation. Furthermore, exchange bias is studied in the fully epitaxial bilayer system. We find a rather strong ferromagnetic exchange bias. The strength of the exchange bias can be estimated by using a simple partial domain wall model. The diluted magnetic semiconductor (DMS) GaMnAs is a promising material for semiconducting spintronic devices. However, the record values of the Curie temperature seem to stagnate below 200 K 6 with no clear strategy to further increase it above room temperature.A novel route toward increasing the ordering temperature is to engineer the material using ferromagnetic metal overlayers. Tuning the magnetic properties at FM metal/DMS-based interfaces based on the most representative DMS system (Ga,Mn)As 7 has recently been explored in a variety of experiments. For example, exchange bias is observed in MnAs/(Ga,Mn)As bilayers. [8][9][10] In contrast, NiFe/(Ga,Mn)As bilayers show an independent magnetization behavior 11 with no exchange bias. In the Fe/(Ga,Mn)As system, the Fe overlayer induces a proximity polarization antiparallel to the Fe moment within a 1-2 nm (Ga,Mn)As region, which is promising for improving the ferromagnetic properties of very thin (Ga,Mn)As films. [12][13][14] In fact, we have recently demonstrated that the proximity effect effectively enhances the operation temperature of Fe/(Ga,Mn)As hybrid spin injection devices when very thin (Ga,Mn)As injector and detector contacts are capped by an iron layer. 15 However, to take full advantage of the control of the magnetization of the (Ga,Mn)As injector/detector contacts, it is of importance to understand the coupling mechanism in this epitaxial FM metal/DMS bilayer system. Here we map out the influence of the (Ga,Mn)As thickness in fully epitaxial Fe/(Ga,Mn)As heterostructures on the interfacial coupling as well as on the magnetization properties of the bulk layer by a combined study using element-specific x-ray magnetic circular dichroism (XMCD) measurements and bulk-sensitive superconducting quantum interference device (SQUID) magnetometry. By means of XMCD we are able to identify a thickness dependent reorientation transition of the Mn magnetization from antiparallel to paral...

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“…3. Note that the associated switching fields cannot directly be compared as coercive fields of extended films (for SQUID) and of micropatterned contact strips (for spin injection) are different [25,26]. To determine T C with SQUID magnetometry, we measured the T dependence of the magnetic moment mðTÞ at 10 mT, shown in Fig.…”

Section: Prl 107 056601 (2011) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 99%

Proximity Induced Enhancement of the Curie Temperature in Hybrid Spin Injection Devices

et al. 2011

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We investigate the increase of the Curie temperature T C in a lateral spin injection geometry where the ferromagnetic (Ga,Mn)As injector and detector contacts are capped by a thin iron film. Because of interlayer coupling between Fe and (Ga,Mn)As T C gets enhanced by nearly 100% for the thinnest (Ga,Mn)As films. The use of the proximity effect might pave the way for practical implementation of spintronic devices. DOI: 10.1103/PhysRevLett.107.056601 PACS numbers: 72.25.Àb, 75.30.Et, 75.50.Pp, 85.75.Àd The diluted magnetic semiconductor (DMS) (Ga,Mn)As [1] stands out as a seminal spintronic material due to its high spin polarization [2,3] and superior interfacing properties with nonmagnetic semiconductors. This opens a way to semiconducting spintronic devices with functionalities such as nonvolatility and the additional spin degree of freedom [4]. However, the persistently low Curie temperature of DMS has been an obstacle for the integration of DMS into electronic devices. It has been recently shown that the presence of a thin layer of Fe couples the magnetic moments of Fe and Mn in Fe=ðGa; MnÞAs bilayers up to room temperature (RT), thus well exceeding the T C of (Ga,Mn)As [5][6][7]. This proximity polarization leads to an antiparallel coupling of the Fe and Mn moments within an interfacial region of a few nm thickness in the (Ga,Mn)As film. In addition, exchange bias has been observed in the Fe=ðGa; MnÞAs bilayer system at lower temperatures T [7]. Similar exchange bias has been obtained in MnAs= ðGa; MnÞAs bilayers [8][9][10]. Differently, NiFe=ðGa; MnÞAs bilayers switch their magnetization independently [11] and also MnTe=ðGa; MnÞAs heterojunctions did not show exchange bias [12]. Here we use the interlayer coupling between Fe and (Ga,Mn)As to explore its impact on the operation temperature of (Ga,Mn)As based spin injector or detector contacts in a lateral transistorlike geometry.The experiments described below demonstrate enhanced spin injection temperatures measured in an all-electrical fashion.The heterojunctions were grown by molecular-beamepitaxy (MBE) on (001) GaAs substrates and consist of a 1000 nm thick n-type transport channel, doped with 4 Â 10 16 cm À3 Si, a 15 nm thin n ! n þ GaAs transition layer (n þ ¼ 5 Â 10 18 cm À3 ), 8 nm n þ -GaAs, and 2.2 nm low-temperature (LT)-grown Al 0:36 Ga 0:64 As, serving as a diffusion barrier, followed by LT-grown Ga 0:95 Mn 0:05 As, the thickness of which was chosen between 5 and 20 nm. The highly doped ðGa; MnÞAs=GaAs pn junction forms an Esaki diode [13,14]. In a next step the wafers were transferred, without breaking vacuum, into an attached metal-MBE chamber, where 2 nm of Fe, corresponding to 14 monolayers (MLs), were epitaxially grown at RT, and finally covered by 4 nm (20 MLs) of Au. The lateral channel of the devices was made by standard lithographic techniques. Electron beam lithography was used to pattern the Fe=ðGa; MnÞAs injector and detector contacts, oriented along the [110] direction, i.e., the easy axis of Fe. A schematic of the sample layout ...

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Mapping the magnetic anisotropy in (Ga,Mn)As nanostructures

Cited by 17 publications

References 15 publications

Electric tuning of magnetization dynamics and electric field-induced negative magnetic permeability in nanoscale composite multiferroics

Electric tuning of magnetization dynamics and electric field-induced negative magnetic permeability in nanoscale composite multiferroics

Reorientation transition of the magnetic proximity polarization in Fe/(Ga,Mn)As bilayers

Proximity Induced Enhancement of the Curie Temperature in Hybrid Spin Injection Devices

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